1. Field of the Invention
This invention relates to vacuum or suction cleaners and more particularly to high efficiency vacuum cleaners, preferably incorporating multiple filter stages, in which the initial filter stage is self-cleaning by reason of the use of a particularly designed relatively coarse mesh filter material positioned over a debris or particulate collection chamber, preferably containing an impervious dust or particulate collection bag.
2. Description of the Prior Art
A large number of so-called vacuum or suction cleaners have been designed in the past. Such cleaners have usually involved the use of rotary fan means to either draw dust laden air through a perforate filter medium such as a cloth bag or the like or to blow dust laden air into a filter such as a filter bag. Particles of dust or other debris are caught by the filter material while the air passes through. As additional dust and debris is built up on the filter material, the pores or openings in the filter become partially blocked with dust and other particulates. The resulting accumulation of dust itself eventually becomes a filter of sorts and the efficiency of the filter action at first increases. Beyond a certain point, however, the efficiency of the filter decreases as the filter medium becomes more impervious to air due to a thick layer of dust and other debris accumulated on the surface of the filter. Multiple stage filtering has been used to increase the efficiency of filtering and the length of the filtering cycle, i.e. the length of time between cleaning or emptying the filter. The initial filter medium in such arrangements is usually coarser, or in other words, has larger holes or meshes in it, than subsequent filters. The dust accumulated is in such multiple stage filtering arrangements distributed between the multiple filter mediums with the larger particles being collected on the coarser initial filter medium or mediums and the smaller particles being caught on the finer filter medium or mediums. This extends the filter cycle of all the filter mediums, but is not always worth the trouble, since there are then more filters to be changed less frequently rather than less filters to be changed more frequently and the trade off is not always advantageous. Of course, the filter stages can be arranged so that the mesh size of one or more of the filters is such that the particular filter accumulates more than its share of particulates and dust so only one filter at a time usually has to be changed or cleaned. This, however, essentially defeats the original aim of increasing the number of stages in the filter cycle.
Multiple layer filters or filter mediums rather than multiple filters have also been used. Multiple layer filters are comprised usually of somewhat erratically laid fibers or matted fibers, rather than a woven or geometrically oriented fiber arrangement forming a sheet or cloth. Such multiple layer filters have the advantage of being less easily blinded by particulates because the openings can be larger than the particulates to be removed from an air stream. This is because the openings can be larger than the particulates to be removed from an air stream. The opening can be larger because the effective passages, or openings, provided through the filter medium are tortuous with the result that particulates impact the various fibers of the filter medium as such particulates are carried through the tortuous passages by the air stream. The particulates are consequently removed from such air stream by their impacts with the fibers, either by adhering to the fibers or becoming entangled in multiple fibers.
So-called filter aids are also sometimes used with a filter to increase the filtering efficiency. Such filter aids, which are usually fibrous in nature, are placed upon a filter and, in effect, convert a single layer filter to a multiple layer filter. They not only enable smaller particulates to be removed from an air stream than might otherwise be possible with the primary filter, but also serve frequently to prevent blinding or clogging of a filter having a relatively small mesh size. Such prevention of blinding and clogging is accomplished by, in effect, holding larger sized particulates away from the smaller filter orifices. Since filter aid materials must be applied periodically to the principal filter, use of such materials is practical usually only for laboratory environments or specialized industrial environments and not readily adaptable for vacuums or suction-type apparatus or cleaners.
Some vacuum or suction systems have also provided cleaning means such as scrapers, rappers, backflow systems and the like to aid in cleaning the filters and particularly an initial coarse filter, but such arrangements add considerable complication to the apparatus. Thus, while the filter cycle may be lengthened, the extra expense and complication is a considerable disadvantage. In addition, scrapers and rappers sometimes tend to force dust and dirt through the mesh of the filter causing an overall decrease in filter efficiency. Such systems also tend to remove a large portion of the accumulation of dust from the filter surface so that a new layer of dust must accumulate before efficient filtering can take place. Some scrapers are arranged only to remove a certain portion of the dust accumulation by passing the scraper along the filter at a predetermined distance from the filter surface. However, this type of arrangement tends to compact the remaining particulate accumulation on the filter at the same time and this interferes with the efficiency of the filter. Backflow-type arrangements which periodically force dust layers from the filter surface are inefficient since the vacuum or suction filtration cycle cannot operate while the backflow is operating and the time available for actual cleaning or suction is thus considerably decreased. While a judicious selection of filter stages may alleviate many of the above enumerated difficulties, the principal difficulty of intermittent operation due to the necessity of periodically cleaning one or more of the filters remains. The following U.S. patents are examples of the present stage of the prior art as described above.
U.S. Pat. No. 2,198,568 issued Apr. 23, 1950 to E.H. Yonkers discloses a self-cleaning suction cleaner which uses a filter medium sold under the name of Dextilose. The filter material is treated with viscose to form a smooth satin finish. The viscose coating prevents adhesion of dust to the filter medium so that "a heavy accumulation of dust and dirt is not possible, the dust and dirt flaking off from the action of gravity aided by the draft of incoming air and falling into the container below." The filter thus tends "to maintain itself in a clean condition."
U.S. Pat. No. 2,295,984 issued Sep. 15, 1942 to B.C. Wilson discloses a shop-type vacuum in which air enters a canister where it drops out a considerable amount of its particulate matter which is thereby removed and the air then passes upward into an inverted filter and removes additional particulates. The filtering cylinder or bag collapses each time the cleaner is shut off so the accumulation of dirt falls into the lower portion of the canister leaving the filter bag free to pass a maximum amount of air when the cleaner is again activated.
U.S. Pat. No. 2,713,921 issued July 26, 1955 to J. Turner discloses a filtering arrangement in which a spiral wiping bar wipes the inside of a cylindrical filter medium to remove accumulated dust. The wiping spiral leaves a sufficient build-up of particulate material on the filter to allow the filtering of finer particles to continue. Turner is only one example of a large number of prior devices for physically removing dust from filter surfaces.
U.S. Pat. No. 3,653,189 issued Apr. 4, 1972 to Y. Miyake, et al. discloses a two-stage filter vacuum cleaner. The initial discussion in the patent discloses that in order to allow a longer vacuum period it has previously been known to use a two-stage filtering system comprising a dust collecting receptacle with a filtering screen of relatively large mesh size and a second fine mesh size filtering medium located immediately down-stream from the first coarse filtering screen. The invention of the patent involves a two-stage filtering arrangement including a first coarse filter screen made of plastic material, fine metal wires or the like and having a relatively large mesh size. Immediately behind is a main filtering means comprising a filter cloth having a fine mesh size which collects the finer dust particles. Also disclosed is a vibrator for use in shaking the dust from the main filter cloth.
U.S. Pat. No. 3,609,946 issued June 28, 1968 to H. Nakagawa et al. discloses a two-stage electric suction cleaner including a relatively coarse mesh filter and a finer mesh filter. As disclosed, the coarse filter is less susceptible to clogging and the finer mesh filter does not have to handle as much dust as it would in the absence of the coarse filter. The period of cleaning is thus increased. As disclosed, the size of the holes, particularly in the coarse filter, is closely related to the period of efficient dust collection. This relationship is shown in the graph in FIG. 8 of the patent. FIGS. 10, 11 and 12 disclose a dual arrangement including two concentric bag or cylinder-type filter means.
U.S. Pat. No. 3,653,190 issued Apr. 4, 1972 to W.J. Lee et al. discloses a vacuum cleaner arrangement including a lower canister which may be lined with a plastic bag or bags to receive detritus dropped from a series of upper filter mediums. A vacuum arrangement is provided in the walls and bottom of the canister to hold the plastic bag against the sides of the canister.
U.S. Pat. No. 3,835,626 issued Sep. 17, 1974 to Y. Miyake, et al. discloses a two-stage vacuum cleaner incorporating a first relatively coarse mesh adjacent a dust storage chamber followed by a conventional cloth filter which accomplishes the final filtering of fine dust particles. The initial filter screen may be made of plastic materials, fine metal wire, or the like and has a relatively large mesh size. The second filter means is in the form of a dust collecting bag made from cloth or the like for collection of fine dust particles. The two-stage filtering arrangement provides longer time periods between filter cleaning cycles.
While prior devices such as shown in the Yonkers 2,198,506 patent, where the filter medium is smooth and non-adherent so large accumulations of dust cannot form, and the Wilson patent 2,295,984 where the filter collapses at the ends of a suction cycle causing dust to be ejected, are in effect self-cleaning, such devices have not proved completely satisfactory since in most cases too much dust is removed, seriously decreasing the efficiency of the filtering action and in the case of the Wilson arrangement the filter cleaning cycle only occurs when the filtering cycle is interrupted.